Field of the Invention
The invention relates to a perfector press for two-sided printing of sheets, wherein sheets are able to be printed on both sides thereof by multi-color printing in just one pass, no recto-/verso-printing or first form/perfector changeover or conversion devices and no turning devices for the sheets being provided.
Such non-convertible perfector presses operate preponderantly in accordance with the so-called blanket-to-blanket principle. In such a case, a printing unit for offset printing is formed of two plate cylinders and two rubber-blanket cylinders, one of which serves as an impression cylinder for the other. When two-sided multicolor printing is provided, a plurality of printing units may be arranged in-line in accordance with the unit construction principle. A feeder is disposed before the first printing unit and a delivery is disposed after the last printing unit. In-line printing presses are voluminous, elaborate and costly.
All of the sub-units of an in-line printing press are fixedly interconnected and are disposed on a common base. The construction of such a printing press remains unchanged throughout its entire service life. The connection between the sub-units can be undone only for the purpose of repairing or replacing one of the sub-units. During such time, the entire printing press is rendered inoperative.
In contrast therewith, satellite printing presses for offset printing are of compact construction. By disposing more than two blanket-cylinder and plate-cylinder pairs around a common impression cylinder, the number of sheet-conveying cylinders and other devices is reduced with respect to printing presses having an in-line arrangement.
In conventional satellite printing presses, the number of blanket-cylinder and plate-cylinder pairs around an impression cylinder is limited to four for reasons of accessibility to the printing units, so that, in a satellite printing unit, a sheet can be printed with four colors on one side. (German Published Prosecuted Patent Application 12 35 953, German Patent 441 329, German Patent 443 399, and U.S. Pat. No. 4,936,211)
German Published Prosecuted Patent Application 12 35 953 describes a sheet-fed rotary offset printing press of satellite construction for selective recto/verso, i.e., first form and perfector, printing and purely one-sided printing wherein, by varying the engagement of the blanket cylinders, two-color recto-and-verso printing, four-color single-sided printing or three-color recto printing and one-color verso printing are possible.
In none of the conventional satellite printing presses for printing sheets is four-color or more than four-color recto-and-verso printing in one pass provided. Only in the case of web-fed printing presses is it known for two satellite printing units to be disposed one above the other in a tower arrangement. The printing-unit tower disclosed in German Published Non-prosecuted Application DE 39 39 432 A1 permits four-color recto-and-verso printing on web stock. Tower-type printing presses require relatively high production rooms or spaces.
Also in the case of tower-type web-fed printing presses, the sub-units are fixedly connected to one another. No provision is made for a flexible combination of the sub-units with one another and with the sub-units of other printing presses located in the same printing shop.
Published European Patent Document EP 0 186 862 A2 describes a device for multi-color printing wherein one machine group causing dead or idle time is releasably connected to the device so that it may be replaced by a second machine group causing dead or idle time. In a satellite-type device, there is a separating line common to all colors which extends between plate cylinders of the movable machine group and the rubber-blanket cylinders in the stationary device. This improves printing-unit accessibility and ensures more-or-less continuous printing operation, because the respective machine group which has been separated can be separately serviced and be made ready for the next job, respectively. Disadvantages thereof, in this regard, are that the printing device is provided only for one-sided printing; there must be two or more of the movable machine groups, so that, in general, the device is voluminous and costly; and the separating line lies in a critical region with regard to register accuracy, so that a reduction in the quality of the printed product must be expected.